This invention relates to lifting magnets and, more particularly to increasing the lifting force and overall performance of the lifting magnet.
Conventional electro-lifting magnets generally have a circular, E shaped in cross section body of ferromagnetic material. The body defines a central core surrounded by outer legs which are spaced from the central core, the core and legs being connected by a yoke. An electrical coil fills the area between the core and legs so that, when the coil is energized electrically, a flux field is generated by magnetic flux flowing between a central pole (the core) and an outer pole (the outer legs) and through the yoke. When the magnet is excited in that manner, it can be used to pick up, and transfer, a load positioned within the flux field. Generally pole shoes are associated with the free ends of the poles to assist in flux distribution in the flux field.
The lifting force of the magnet is dependent upon the amount of flux generated when the magnet is excited which in turn is directly dependent upon, among other things, the ampere-turns of the electrical coil.
Another factor to be considered in evaluating the overall efficiency or performance of the magnet is the ability of the coil to dissipate self generated heat occuring when the magnet is excited. If the coil is able to dissipate this heat, it can operate at a lower temperature and more efficiently or it can operate at higher current level thus increasing the available ampere-turns.
U.S. Pat. No. 3,521,209 is concerned with the general problem of improving the operation of an electro-lifting magnet. That patent suggests replacing a portion of a conventional electric coil, normally made of non-ferromagnetic material, with a ferromagnetic material. Both non-ferromagnetic and ferromagnetic coil portions were energized electrically to excite the magnet.
Among the general objects of this invention is to increase the lifting force of an electro-lifting magnet and/or to increase the overall performance or operating efficiency of the magnet.